Assisted inhibition effect of acetylcholinesterase with n-octylphosphonic acid and application in high sensitive detection of organophosphorous pesticides by matrix-assisted laser desorption/ionization Fourier transform mass spectrometry

A simple and practical approach to improve the sensitivity of acetylcholinesterase (AChE)-inhibited method has been developed for monitoring organophosphorous (OP) pesticide residues. In this work, matrix-assisted laser desorption/ionization Fourier transform mass spectrometry (MALDI-FTMS) was used to detect AChE activity. Due to its good salt-tolerance and low sample consumption, MALDI-FTMS facilitates rapid and high-throughput screening of OP pesticides. Here we describe a new method to obtain low detection limits via employing external reagents. Among candidate compounds, n-octylphosphonic acid (n-Octyl-PA) displays assistant effect to enhance AChE inhibition by OP pesticides. In presence of n-Octyl-PA, the percentages of AChE inhibition still kept correlation with OP pesticide concentrations. The detection limits were improved significantly even by 102–103 folds in comparison with conventional enzyme-inhibited methods. Different detection limits of OP pesticides with different toxicities were as low as 0.005 μg L−1 for high toxic pesticides and 0.05 μg L−1 for low toxic pesticides. Besides, the reliability of results from this method to analyze cowpea samples had been demonstrated by liquid-chromatography tandem mass spectrometry (LC–MS/MS). The application of this commercial available assistant agent shows great promise to detect OP compounds in complicated biological matrix and broadens the mind for high sensitivity detection of OP pesticide residues in agricultural products.

In the presence of n-octylphosphonic acid, the percentage of AChE inhibition caused by acephate pesticide was increased significantly. The enzyme inhibition still kept correlation with acephate concentrations. Monitoring of enzyme reaction and screening enzyme inhibitor in cowpea samples were based on MALDI-FTMS.Figure optionsDownload as PowerPoint slideHighlights
► n-Octylphosphonic acid enhanced enzyme inhibition by organophosphorous pesticide.
► The detection limits were much lower than those of other enzymatic methods.
► This approach was applied in cowpea samples and confirmed by standard method.